Maybe it would mean that? I see the logic, we have more vaccines and cures now so to reach the same risk there would need to be more sex, according to the theory.

But it doesn't mean it is increasing now or that it generally increases over time.

As the risk of stds fluctuate, so would promiscuity, albeit with a time displacement and inversely of course.

So that's what the hypothesis would predict. A steep decrease in promiscuity following a pandemic, and then a gradual growth as a cure for it or vaccine is found.

Regarding the present time. I think we would be in a promiscuous phase, yes, the std risks are quite low.

Evidence? How about dropping marriage and increasing divorce rates? Divorces even peak in the aids pandemic. The effect of cures for gonorrhea ,clam etc.. I don't know exact dates, but generally it does coincide that we've been curing them for the past century and marriage is becoming less prevalent.